1. Field of the Invention
The present invention relates to a position tracing system, and more particularly, to a position tracing system using ultrasonic wave.
2. Description of the Related Art
In the related art, a position tracing system which traces a position of an input pen generating an ultrasonic wave signal measures a distance between the input pen and each of two ultrasonic wave reception sensors by using a difference between reception times of the ultrasonic wave signal and a reference signal (for example, an infrared signal or an RF signal) generated by the input pen and measures the position of the input pen by using a predetermined distance between the ultrasonic wave reception sensors and the measured distance between the input pen and each of the ultrasonic wave reception sensors. An example of the position tracing system using an ultrasonic wave signal is disclosed in Korean Patent No. 10-0418423.
In the position tracing system in the related art, ultrasonic wave reception sensors which receive the ultrasonic waves may be included inside a single housing or fixed to a predetermined position, so that the distance between the ultrasonic wave reception sensors may be maintained constant.
In the case where the distance between the ultrasonic wave reception sensors has a fixed value, since an accurate value of the distance between the ultrasonic wave reception sensors is known, the length of one side among three sides of a triangle, which is constructed with an input pen and the two ultrasonic wave reception sensors, for calculating the position of the input pen is fixed as a constant value, so that there is an advantage in that the position tracing system can be used without calibration.
However, in the case where the ultrasonic wave reception sensors are installed inside one housing, there is a limitation in that the distance between the ultrasonic wave reception sensors cannot be increased so as for the housing to be easy to carry or install.
In the case where the distance between the ultrasonic wave reception sensors is small and a moving area of the input pen is wide, if the input pen generates the ultrasonic wave signal at a position far from the ultrasonic wave reception sensors, the triangle which is constructed with the input pen and the two ultrasonic wave reception sensors becomes an acute triangle having a very small acute angle. If the angle is small, an error occurring in the calculation is relatively large, so that an error caused by external environment factors is more greatly reflected.
Therefore, in the case where the input pen is located at the position far from the ultrasonic wave reception sensors, the error of coordinates is increased due to the external environment factors (wind, a change in temperature, or other factors changing the speed of ultrasonic wave), so that resolution of the position tracing system is deteriorated. In order to solve the above-described problem, the distance between the ultrasonic wave reception sensors may be set to be large so as to correspond to the size of the moving area of the input pen. However, if the distance between the ultrasonic wave reception sensors is increased, the entire size of the housing is also increased, so that the position tracing system is not easy to carry. Accordingly, in this case, there is a problem in that the distance between the ultrasonic wave reception sensors cannot be increased.